This supplemental application requests additional funds for personnel, equipment and subject costs to facilitate the collection of developmental data on speech perception by human infants. The original goals of grant HD-11915-03 remain intact, except for the addition of a high amplitude sucking lab to complement the operant head-turning lab currently in operation. A series of experiments are proposed for investigating the manner in which prelinguist infants process speech and speech-like acoustic stimuli. Discrimination data will be obtained from two- to eighteen-month old infants for synthetic and natural speech sounds as well as for nonspeech stimuli generated to match the complex temporal and frequency relations present in speech. Measurement of discrimination will be performed using either a high amplitude sucking procedure or an operant conditioning procedure. Identification will be assessed in the older infants by three modifications of the simple discrimination paradigm using either a head-turning or a button-pressing technique. Major variables of interest are the perception of the acoustic cues for voicing and place of articulation in stop consonants, the perception of the acoustic cues for vowels, and the influence of the surrounding context and the phonetic environment on the perception of stop consonants and vowel categories. In addition, several experiments are aimed at determining whether infants show perceptual constancy for stop consonants and vowels containing radically different acoustic cues. Results from these studies will provide important evidence for evaluating several recent claims that speech sounds are processed in a specialized perceptual mode and that the perceptual system of infants is innately attuned to analyze speech sounds in a language-specific manner.